This invention relates to an amorphous magnetic alloy adapted to, for example, a magnetic core of a magnetic head. To date, Permalloy, ferrite or Sendust has been used as the crystalline core of a magnetic head. However, Permalloy has the drawbacks that though it possesses good soft-magnetic properties and machinability, it has a relatively low saturation magnetic flux density, low electric resistance, and consequently a low A.C. magnetic permeability, and a low abrasion resistance due to its softness. The ferrite also has the drawback that though it possesses an excellent high frequency property due to its high electric resistance and also a great abrasion resistance due to its hardness, yet it has a low saturation magnetic flux density, which presents difficulties in machining due to its hardness and brittleness, and gives rise to problems with respect to corrosion resistance because it mainly consists of iron.
Recently, attention has been drawn to a pure amorphous magnetic material, in place of a crystalline magnetic material. The amorphous magnetic material has been actively used in various applications. The amorphous magnetic material has the following characteristics.
(a) The amorphous magnetic material has no crystalline anisotropy, and, when its composition is free from magnetostrictions, it indicates as high a magnetic permeability .mu. as Permalloy.
(b) When alloyed with, for example, chromium or molybdenum, the amorphous magnetic material has higher corrosion resistance than stainless steel.
(c) The amorphous magnetic material has great hardness and indicates as high an abrasion resistance as Sendust.
(d) The amorphous magnetic material has high electric resistance and is generally produced with as small a thickness as about 40 microns, and consequently indicates high magnetic permeability .mu. in the high frequency region.
(e) The amorphous magnetic material indicates relatively high saturation magnetic flux density of about 7 to 9 kilogausses.
Patent disclosure No. 51-73920 may be cited as a published information describing an amorphous alloy of high magnetic permeability. The disclosed amorphous magnetic material has a typical composition of Fe.sub.5 Co.sub.70 Si.sub.15 B.sub.10. The amorphous magnetic material has a more metastable state than a crystalline magnetic material. The amorphous magnetic material is generally crystallized at a temperature (hereinafter referred to as "a crystallization temperature Tx") of 400.degree. to 500.degree. C., and loses its soft magnetic property. Consequently, the amorphous magnetic material is desired to have as high a crystallization temperature Tx as possible. The disclosed amorphous magnetic material having a composition of Fe.sub.5 Co.sub.70 Si.sub.15 B.sub.10 has a relatively high crystallization temperature Tx of about 500.degree. C. However, an amorphous magnetic material is demanded to have a higher crystallization temperature Tx in order to have a higher thermal stability. Said amorphous magnetic material whose composition is represented, for example, by Fe.sub.5 Co.sub.70 Si.sub.15 B.sub.10 lacks a corrosion resistance-improving element such as chromium or molybdenum and does not indicate a high corrosion resistance.